This project will investigate the mechanism of calcium release from the sarcoplasmic reticulum of skeletal muscle. The experiments will be conducted with "skinned" (sarcolemma removed) fibers treated with voltage sensitive dyes. This preparation will allow the ionic conditions surrounding the SR to be manipulated by the experimenter. In addition, the optical signals recorded during calcium release will offer a direct measure of SR membrane potential changes. The potassium ionophore valinomycin will be used to increase the resting potassium conductance of the SR. Changes in the potassium concentration of the bathing media can then be used to impose voltage changes of known amplitude on the SR membrane. The amplitude of these applied voltage changes will be calculated using the Nernst equation. Optical signals will be measured using differential wavelength recording to reduce the effects of wavelength independent optical noise. The aims of the project are to determine the relationship between the voltage imposed across the SR membrane and the amount of calcium released, to investigate the existence of counterions which flow during or shortly after calcium release, and to test the dependence of the release process in skinned fibers on the existence of a potential change in the SR. The results should lead to an increased understanding of the membrane events which occur during calcium release from the SR and of the regulatory processes involved in excitation-contraction coupling.